Light-emitting semiconductor devices may be arranged in various configurations, such as arrays, for lighting applications. These applications generally have associated parameters (e.g., a photoreaction may entail provision of one or more levels of radiant power, at one or more wavelengths, applied over one or more periods of time). In these applications, the light emitting semiconductor devices generally are employed to provide radiant output and otherwise operate in accordance with various, desired characteristics, e.g., temperature, spectral distribution and radiant power. At the same time, the light emitting semiconductor devices typically have certain operating specifications, which specifications generally are associated with the light emitting semiconductor devices' fabrication and, among other things, are directed to preclude destruction and/or forestall degradation of the devices. These specifications generally include operating temperatures and applied, electrical power.
Arrays of light emitting semiconductor devices have been constructed which provide for monitoring selected of the array's characteristics. Providing such monitoring enables verification of the array's proper operation and, in turn, determination as to whether the array is operating in any way other than properly. An array may be operating improperly with respect to either/both the application's parameters or/and the array's specifications.
Monitoring also supports control of an array's operation. Control, in turn, may be employed to enable and/or enhance the array's proper operation and/or performance of the application. Monitoring the array's operating temperature and radiant output supports control of the array, directly or indirectly, including through adjustment(s) in applied power and cooling (such as through a systemic cooling system). This control may be employed to enable and/or enhance balance between the array's radiant output and its operating temperature, so as, e.g., to preclude heating the array beyond its specifications.
Using control of the array in enabling/enhancing performance of an application may be illustrated via example. In this example, an array is used that is understood to include light emitting diodes (LEDs). Moreover, the application is understood to require provision, in sequence, of light in the red, then green and then blue spectra, at three respective energy levels, while maintaining a select temperature range relating to the work piece. In performing this application, control may again be directed to the array's applied power and to cooling, e.g., by a systemic cooling system. The control is again responsive to the monitoring of the array's operating temperature and radiant output. With this monitoring, the system is enabled to sense the energy applied to the work piece for the first wavelength, compare that energy to the respective energy level, while continually monitoring the temperature. If the temperature approaches its maximum, control may be employed to increase cooling, to decrease the radiant power, or both, while continuing to gauge the applied energy. Once the energy level for the first wavelength is reached, control powers off the LEDs associated with the first wavelength and powers on the LEDs associated with the next sequential wavelength, and so on.
Conventional approaches for monitoring and controlling an array typically propose to mount detectors around the array's perimeter or otherwise proximate to, but separate from the array. In doing so, the detectors detect radiant output or temperature associated with the whole, or relatively large portions of, the array. Moreover, responsive to such detection, the array generally is controlled as a whole, or in relatively large portions. Also, conventional industry approaches may use various detectors, alone or in combination: in some cases, only photo detectors are used; in other cases, only temperature sensors are used; in still other cases, both photo detectors and temperature sensors are used and, in still other cases, some other combination of detectors is used.
An example of conventional monitoring and control of a LED array is found in U.S. Pat. No. 6,078,148, to Hochstein, entitled Transformer Tap Switching Power Supply For LED Traffic Signal (the “'148 Patent”). The '148 Patent, generally, proposes to monitor and control a traffic signal's LED array using a single LED light detector, together with a controller, wherein the LED light detector is disposed proximate to the array (but not part of the array) so as to measure the luminous output of (i) one or more of the array's LEDs or (ii) a so-called “sample” LED which is not part of the array, but performs similarly. Responsive to that measurement, the '148 Patent proposes that the controller provide for selection from among a plurality of taps of a transformer, thereby adjusting the voltage applied to the LED array as a whole and maintaining the luminous output of the traffic signal's LED array. The '148 Patent also proposes (a) provision of a measurement device for measuring the temperature of the LED array generally, (b) selection of a tap responsive to such measurement and (c) associated adjustment of the voltage applied to the LED array as a whole.
Another example of conventional monitoring and control of a LED array is found in U.S. Pat. No. 6,683,421, to Kennedy et al., entitled Addressable Semiconductor Array Light Source For Localized Radiation Delivery (the “'421 Patent”), the contents of which are hereby incorporated by reference as if recited in full herein, for all purposes. The '421 Patent proposes to monitor and control a photoreaction device that includes a LED array, a photo sensor and a temperature sensor. The photo sensor is proposed to preferably comprise semiconductor photodiodes that provide continuous monitoring of the light energy delivered to a work piece, so that irradiation may be controlled.
In one embodiment of the '421 Patent, the LED array is proposed to have an associated output window positioned above the LED array. The output window is proposed to be selected so that a small percentage of the LED array's light energy (typically less than 10%) is internally reflected within the window. This internally reflected light is proposed to be measured by the photo sensor. Not only is this reflected light measured, it is expressly specified that this configuration minimizes or prevents light energy reflected from the work piece or from external sources from being detected by the photo sensor. In order to measure the internally reflected light, the photo sensor is proposed to be positioned and configured for that function, e.g., using a series of photo sensors positioned around the perimeter of the output window. Moreover, it is expressly specified that this measurement using the series of photo sensors will detect changes in average optical power.
This embodiment has disadvantages. As an example, only average optical power is detected. That is, the window captures the internally reflected light from the entire array, which captured light is provided to the sensors. Accordingly, the sensors cannot determine where the LED array's radiant output may be improper and, as such, cannot make adjustments except across the entire array. As well, by seeking to minimize or prevent detection of light energy reflected from the work piece or from external sources, control based on such light energy is precluded.
In another embodiment, the '421 Patent proposes to employ optical fibers between columns of LEDs in the array. The '421 Patent proposes that these fibers, preferably, will be made of material which is able to receive sidewall light emissions from the LEDs of the adjacent column of the LED array. The '421 Patent further proposes that, as to each fiber, the received sidewall light emissions are directed through internal reflection toward a respective photo sensor, the photo sensor being positioned at the perimeter of the array, disposed at the end of the fiber. Apparently, as in the previous embodiment, each photo sensor will measure such light, detecting changes in average optical power.
This embodiment has disadvantages. Again, only an average optical power is detected. Average optical power is again understood in that each fiber captures internally reflected light from the plurality of LEDs disposed across an entire dimension of the array, which captured light is provided to the respective sensor. The respective sensor cannot determine where the LED array's radiant output may be improper across the implicated dimension and, as such, cannot make adjustments except across the entire set of LEDs associated with that fiber. In addition, because the fibers are disposed among the LEDs, in the plane of the array (i.e., so as to capture sidewall light emissions), use of the fibers precludes or degrades use of optics that, desirably, collect and collimate all or substantially all of the radiant output of each LED (such optics include, e.g., a grid of reflectors as proposed by the '421 Patent or a plurality of micro-reflectors in which individual LEDs are mounted, preferably on a one-to-one basis). As well, by detecting only sidewall light emissions, control based on detecting other light energy associated with the array is precluded.
In yet another embodiment, the '421 Patent proposes to position about a LED array a temperature sensor and a plurality of photo detectors. However, the '421 Patent omits to describe the disposition of the temperature sensor or the photo detectors relative to the plane of the LED array. It may be inferred that, as in the embodiment set forth above, the photo detectors are positioned above the array in association with a light guide, e.g., an output window. This inference follows as the '421 Patent expressly specifies that the LED die are arranged in a shape approximating a “filled square”, which arrangement would leave no space for the temperature sensor or the photo detectors in the plane of the LED array.
This embodiment has disadvantages. With photo detectors positioned in association with the output window, disadvantages include those set out above respecting other embodiments using light guide(s) to collect detected output radiation. On the other hand, if a sensor or photo detector were placed in the LED array's plane, the sensor or detector would be disposed between the rows and columns of the LED array, contemplating having substantial space between the LEDs of the array. Such space generally is not desirable (i.e., typically, it is desirable to employ densely-packed LED arrays, wherein space between rows and columns of LEDs typically is insufficient to accept interposition of a semiconductor device, such as conventionally-sized sensor or detector).
In still another embodiment, the '421 Patent proposes to group the LEDs of the array into alternating rows, such that the odd rows would form one group and the even rows would form a second group. The '421 Patent further proposes that the odd rows would be energized as a group to emit light energy, including sidewall light emissions, and that the even rows would function, as a group, as a photo sensor (i.e., by generating a current proportional to the intensity of the impinging sidewall light emissions from the one group of odd rows). The '421 Patent further proposes that, the respective functions of the odd and even rows may be switched, so that the odd rows operate as the detecting group, while the even rows operate as the emitting group.
This embodiment has disadvantages. Again, average optical power is detected. Average optical power is again understood in that the detecting LEDs, as a group, detect the sidewall light emissions from the emitting group, which emitting group includes all the LEDs of all non-detecting rows of the entire array. The detecting group of LEDs cannot determine where the LED array's radiant output may be improper across any one or more rows of the emitting group and, as such, cannot make adjustments except for the entire group of emitting LEDs. As well, by detecting only sidewall light emissions, control based on detecting other light energy associated with the array is precluded. In addition, because of the potential for relatively substantial reduction of radiant output, it is generally not desirable to use any entire row in the LED array solely to detect, let alone using half of all rows of the LED array for detection.
Accordingly, there is a need for apparatus, systems and methods that employ detectors to monitor selected characteristics of a light emitting semiconductor devices, such as LED arrays. In addition, there is a need for such apparatus, systems and methods that so monitor, while minimizing or eliminating impact on the radiant output that otherwise might result from provision of detectors and related devices and/or structure. Moreover, there is a need for such apparatus, systems and methods that respond to variations and improvements in the light emitting semiconductor devices, including, as examples, where each LED of an LED array is mounted in a respective micro-reflector that collects and collimates the mounted LED's light and/or where the LED array is a dense array. Moreover, there is a need for such apparatus, systems and methods that respond to the applications employing such light emitting semiconductor devices, including, as examples in use of an LED array, by characterizing the LED array's operating characteristics specific to the application and/or by providing for control of the LEDs so as to enable or enhance performance of the application. Generally, there is also a need for apparatus, systems and methods that employ detectors to monitor and enable control of selected characteristics of light emitting semiconductor devices, such as LED arrays and, in doing so, avoid entirely or substantially the disadvantages associated with conventional approaches.